Monoalkylbenzene can be used in the preparation of alkyl phenyl hydroperoxide. For example, ethylbenzene hydroperoxide can be prepared by the oxidation of ethylbenzene with oxygen containing gas, such as air. Such oxidation processes are well known in the art. An example thereof is described in U.S. Pat. No. 5,883,268. Other well-known processes wherein alkyl phenyl hydroperoxides are produced, are those wherein iso-propylbenzene (cumene) or sec-butylbenzene are oxidised, using oxygen containing gas, into the corresponding alkyl phenyl hydroperoxides.
Cumene hydroperoxide can subsequently be decomposed into phenol and acetone. Ethylbenzene hydroperoxide can subsequently be used in the oxidation of an alkene, such as propene, resulting in the production of alkene oxide (an oxirane or epoxide), such as propylene oxide, and methyl phenyl carbinol which is 1-phenylethanol. Methyl phenyl carbinol can then be dehydrated into styrene. Both the styrene and the propylene oxide are valuable market products.
Processes for the joint preparation of styrene monomer (“SM”) and propylene oxide (“PO”) are known in the art and are commonly referred to as “SM/PO” or “PO/SM” processes. An SM/PO process is for example described in WO200005186. In general, an SM/PO process comprises the steps of:    (a) reacting ethylene and benzene to form ethylbenzene;    (b) reacting ethylbenzene with oxygen containing gas to form ethylbenzene hydroperoxide;    (c) reacting ethylbenzene hydroperoxide with propene in the presence of an epoxidation catalyst to form propylene oxide and 1-phenylethanol; and    (d) dehydrating 1-phenylethanol into styrene in the presence of a suitable dehydration catalyst.
During said step (b) of oxidising ethylbenzene into ethylbenzene hydroperoxide, not all ethylbenzene reacts. Most of the ethylbenzene leaves the oxidation reactor as solvent for the ethylbenzene hydroperoxide. However, also a substantial portion of the ethylbenzene leaves the oxidation reactor as part of a gas stream comprising oxygen. Said gas stream comprising oxygen and ethylbenzene may be discarded. However, it would be advantageous to recover the valuable ethylbenzene from said gas stream comprising oxygen and ethylbenzene, and then re-use it for some purpose, for example by recycling the recovered ethylbenzene to the oxidation reactor.
However, in addition to oxygen and monoalkylbenzene (for example ethylbenzene) and an inert gas such as nitrogen, such gas stream comprising oxygen, nitrogen and monoalkylbenzene may comprise other contaminants, such as methane, water, acetaldehyde, propionaldehyde, methanol, benzene and toluene. These other contaminants should not be recovered from said gas stream together with the monoalkylbenzene. Therefore, the monoalkylbenzene should be recovered both efficiently and selectively from the gas stream comprising oxygen and monoalkylbenzene. Further, at the same time, in such recovery care should be taken of the presence of oxygen which is a reactive gas and not an inert gas such as nitrogen.
In general, it is known to absorb an organic contaminant from a gas stream comprising oxygen and organic contaminants, by contacting such gas stream with a liquid absorbent. For example, WO2002102496 discloses a process for the recovery of combustible components of a gas stream comprising the combustible components and oxygen by selective absorption of the combustible components in a solvent. The process of WO2002102496 is characterized in that during the absorption the gas phase is dispersed in a continuous liquid phase of the solvent. According to WO2002102496, said solvent (absorbent) may be selected from alcohols, aliphatic and aromatic hydrocarbons and ketones. Further, in Example 1 of WO2002102496, benzene is mentioned as a combustible component. Monoalkylbenzenes, such as ethylbenzene, are not disclosed in WO2002102496.
U.S. Pat. No. 5,198,000 on the other hand discloses a process wherein ethylbenzene is mentioned as one of the organic compounds that can be removed from a gas stream comprising oxygen and organic contaminants. The method of U.S. Pat. No. 5,198,000 is a method for removing volatile organic compounds from a contaminated air stream by contacting the latter with an absorbent to allow absorption of the volatile organic compound by the absorbent. Specific absorbents mentioned in U.S. Pat. No. 5,198,000 are motor oil, vegetable oil, corn oil, mineral oil, olive oil, castor oil, coconut oil, palm oil, peanut oil, safflower oil, soya bean oil, tucum oil, linseed oil and cotton seed oil. Corn oil is particularly preferred as the liquid absorbent of the invention of U.S. Pat. No. 5,198,000. According to U.S. Pat. No. 5,198,000, the source of the contaminated air stream may be off-gas produced by air stripping, flue gases, etc.